As shown in Theorem REF , we only estimate the overall channel \({\bf q}_k \in \mathbb {C}^{M\times 1}\) , which possesses the same dimension as in traditional MISO systems. Therefore, we only require that the length of pilot sequences is larger than the number of users, i.e., \(\tau \ge 1\) . Compared with the estimation method which needs the estimation of all \(MN\)  individual channels[1]}, our method has very low overhead and complexity.
